Choose one release or the other. Per FAQ 15.4.1, you should be using a port tree synchronized to your OS, anyway. OpenBSD 4.6-release was synced to 9.64, 4.7-release to 10.10. At the moment, -current is on 10.11.

Installing ports out-of-sync is unsupported by the project, and that would include, I expect, Nikolay Sturm, this port's maintainer.

In case it is unclear to you, Opera is a closed source program product of Opera Software ASA. The OpenBSD port is nothing more than a packaging of instructions to download and install a precompiled binary, which executes using the Linux emulation ABI available for OpenBSD/i386.